The present invention relates to silver halide photographic emulsion and a process for the preparation thereof.
In the photosensitive materials such as color film, X-ray film and general black and white film or the like for which the high sensitivity is required, silver iodobromide is used and that so-called chemical sensitizing such as reduction sensitization, sulphur sensitization or gold sensitization is applied to the photosensitive materials.
With such chemical sensitizing applied, it is possible to obtain higher sensitivity. At the same time, however, the sensitivity for the red light rises owing to chemical sensitizing alone despite no spectral sensitization applied and the fog takes place when the red safe light is used (U.S. Pat. No. 3,411,914 and Japanese Patent examined Publication No. 8831/1970).
Namely, the operation efficiency under the red safe light which is relatively bright is extremely impeded and unexpected fog problems caused by the safe light may take place during the course of preparing process for photosensitive materials and the course of handling photosensitive materials by the general users, which is dangerous.
As a technology to solve such fog problem caused by the red safe light, there are disclosed some methods in U.S. Patent No. 3,411,914 and Japanese Patent Publication Open to Public Inspection No. 6073/1971 which include a method to add tetrazaindenes on the half way of chemical sensitizing or a method to provide a dye filter layer. These methods, however, have disadvantages that the thermal stability of photosensitive materials deteriorates considerably and the fog caused by the heat increases.
In Japanese Patent Examined Publication No. 8831/1970, on the other hand, there is disclosed a method in which the chemical sensitizing is conducted with gold (I) mercaptide but this method has disadvantages that the thermal stability deteriorates remarkably and the sensitivity drops for the long time exposure under the low illumination thus a low intensity reciprocity law failure takes place.
In Japanese Patent Examined Publication No. 24937/1981, furthermore, there is disclosed a method wherein the chemical sensitizing is conducted with thiosuccinimide compounds but this method does not give a sufficient sensitivity.